Wafer boat handling device, vertical batch furnace and method

ABSTRACT

Wafer boat handling device, configured to be positioned under a process chamber of a vertical batch furnace, and comprising a rotatable table comprising a first and a second wafer boat support surface. Each wafer boat support surface is configured for supporting a wafer boat. The rotatable table is rotatable by an actuator to rotate both the first and the second wafer support surfaces to a load/receive position in which the wafer boat handling device is configured to load a wafer boat vertically from the rotatable table into the process chamber and to receive the wafer boat from the process chamber onto the rotatable table, a cooldown position in which the wafer boat handling device is configured to cool down a wafer boat, and a transfer position for transferring wafers to and/or from the wafer boat.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application Ser. No. 62/848,760 filed May 16, 2019 titled WAFER BOAT HANDLING DEVICE, VERTICAL BATCH FURNACE AND METHOD, the disclosures of which are hereby incorporated by reference in their entirety.

FIELD OF DISCLOSURE

The present disclosure generally relates to a wafer boat handling device. The wafer boat handling device may be configured to be positioned under a process chamber of a vertical batch furnace. The present disclosure furthermore relates to a vertical batch furnace assembly comprising said wafer boat handling device. The present disclosure also relates to a method for handling wafer boats.

BACKGROUND

Wafer boat handling devices may be positioned under a process chamber of a vertical batch furnace. Wafer boat handling devices may be part of a vertical batch furnace and may be configured to vertically transport a wafer boat to a process chamber of said batch furnace, and to receive the wafer boat from the process chamber. The wafer boat received from the vertical batch furnace may be hot and may be cooled down before the processed wafers can be taken out of the wafer boat. The wafer boat handling device may be used to transfer wafers to and from the device, in particular to and from the wafer boats accommodated therein. Some of the functions of the wafer boat handling devices may be effected by a wafer boat carousel which transports the wafer boats.

SUMMARY

This summary is provided to introduce a selection of concepts in a simplified form. These concepts are described in further detail in the detailed description of example embodiments of the disclosure below. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

It may be an object to provide an improved wafer boat handling device.

To that end, the present disclosure provides a wafer boat handling device according to claim 1. More particularly, the wafer boat handling device may be configured to be positioned under a process chamber of a vertical batch furnace. The wafer boat handling device comprises a rotatable table having just a first and a second wafer boat support surface. Each wafer boat support surface may be configured to support a wafer boat. The rotatable table may be rotatable around a central substantially vertical axis and may be rotatable by an actuator to rotate both the first and the second wafer support surfaces to a load/receive position, a cooldown position, and a transfer position. In the load/receive position the wafer boat handling device may be configured to load a wafer boat vertically from the rotatable table into the process chamber and to receive the wafer boat from the process chamber onto the rotatable table. In the cooldown position the wafer boat handling device may be configured to cool down a wafer boat. In the transfer position the wafer boat handling device may be configured to allow wafers to be transferred to and/or from the wafer boat.

The time needed for processing, cooling and transferring may not be equal. When the cooling down is quick, and the transferring is done efficiently, both actions can be performed within the time needed for processing the wafers in the process chamber. The wafer boat handling device therefore may comprise just two wafer boat support surfaces which can be transferred to three rotational positions, in particular the load/receive position, the cooldown position, and the transfer position.

An advantage of having only two wafer boat support surfaces is that the rotatable table can be made smaller compared to having three wafer boat support surfaces. With the three rotational positions in which each wafer boat support surface can be brought, the wafer boat cooldown device can perform the required functions of loading/receiving, cooling down and transferring while the diameter of the wafer boat handling device may be reduced relative to the known wafer boat handling devices having three wafer boat support surfaces on the rotatable table. Additionally, the costs of manufacturing the wafer boat handling device may be smaller than the costs of the wafer boat handling devices with three wafer boat support surfaces.

The present disclosure also relates to a vertical batch furnace assembly according to claim 13. More particularly, the vertical batch furnace assembly comprises a process chamber for processing wafers accommodated in a wafer boat, and a wafer boat handling device according to the present disclosure. The wafer boat handling device may be positioned under the process chamber, and may comprise a wafer boat lift assembly configured to transfer a wafer boat from the wafer boat handling device to the process chamber and vice versa.

The vertical batch furnace may have the same advantages as described above in relation to the wafer boat handling device.

Further, the present disclosure provides a method for handling wafer boats according to claim 15. The method comprises providing a vertical batch furnace assembly comprising a process chamber and a wafer boat handling device which is positioned under the process chamber, wherein the wafer boat handling device is the wafer boat handling device according to the present disclosure. The method further comprises providing the first wafer boat support surface with an associated first wafer boat loaded with wafers and the second wafer boat support surface with an associated second wafer boat loaded with wafers, and loading the first wafer boat vertically from the first wafer boat support surface which is in the load/receive position into the process chamber. The method further comprises processing the wafers accommodated in the first wafer boat in the process chamber, whilst simultaneously cooling down the second wafer boat on the second wafer boat support surface which is in the cooldown position, and subsequent to the cooling down, rotate the rotatable table to a position in which the second wafer boat support surface is in the transfer position. Subsequently, wafers are transferred to and/or from the second wafer boat, and subsequent to the transferring, the rotatable table rotates to a position in which the first wafer boat support surface is in the load/receive position.

The method may have the same advantages as described above in relation to the wafer boat handing device and the vertical batch furnace assembly.

For purposes of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages of the invention have been described herein above. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught or suggested herein without necessarily achieving other objects or advantages as may be taught or suggested herein.

Various embodiments are claimed in the dependent claims, which will be further elucidated with reference to an example shown in the figures. The embodiments may be combined or may be applied separate from each other.

All of these embodiments are intended to be within the scope of the invention herein disclosed. These and other embodiments will become readily apparent to those skilled in the art from the following detailed description of certain embodiments having reference to the attached figures, the invention not being limited to any particular embodiment(s) disclosed.

BRIEF DESCRIPTION OF THE FIGURES

While the specification concludes with claims particularly pointing out and distinctly claiming what are regarded as embodiments of the invention, the advantages of embodiments of the disclosure may be more readily ascertained from the description of certain examples of the embodiments of the disclosure when read in conjunction with the accompanying drawings, in which:

FIG. 1 shows a schematic top view of an example of the wafer boat handling device according to the description, wherein the first wafer boat is placed on the first wafer boat support surface which is in the load/receive position, and wherein the second wafer boat is placed on the second wafer boat support surface which is in the cooldown position;

FIG. 2 shows a schematic top view of the example of the wafer boat handling device according to FIG. 1, wherein the first wafer boat is placed in the process chamber, and wherein the second wafer boat on the second wafer boat support surface is in the transfer position;

FIG. 3 shows a perspective view of an example of the vertical batch furnace assembly;

FIG. 4 shows a schematic top view of the example of the vertical batch furnace assembly according to FIG. 3; and

FIG. 5 show an example of an arrangement of multiple vertical batch furnace assemblies of the example according to FIGS. 3 and 4, e.g. in a semi-conductor manufacturing plant.

DETAILED DESCRIPTION OF THE FIGURES

In this application similar or corresponding features are denoted by similar or corresponding reference signs. The description of the various embodiments is not limited to the example shown in the figures and the reference numbers used in the detailed description and the claims are not intended to limit the description of the embodiments, but are included to elucidate the embodiments by referring to the example shown in the figures.

Although certain embodiments and examples are disclosed below, it will be understood by those in the art that the invention extends beyond the specifically disclosed embodiments and/or uses of the invention and obvious modifications and equivalents thereof. Thus, it is intended that the scope of the invention disclosed should not be limited by the particular disclosed embodiments described below. The illustrations presented herein are not meant to be actual views of any particular material, structure, or device, but are merely idealized representations that are used to describe embodiments of the disclosure.

As used herein, the term “substrate” or “wafer” may refer to any underlying material or materials that may be used, or upon which, a device, a circuit, or a film may be formed.

FIG. 1 shows a schematic top view of an example of the wafer boat handling device 10, configured to be positioned under a process chamber 56 of a vertical batch furnace for processing wafers accommodated in a wafer boat 12, 14. The wafer boat handling device 10 comprises a rotatable table 16 having just a first and a second wafer boat support surface 18, 20. Each wafer boat support surface 18, 20 is configured for supporting a wafer boat 12, 14. The rotatable table 16 may be rotatable by an actuator around a central substantially vertical axis 22 to rotate both the first and the second wafer support surfaces 18, 20 to a load/receive position 24, a cooldown position 26, and a transfer position 28.

In the load/receive position 24 the wafer boat handling device 10 may be configured to load a wafer boat 12, 14 vertically from the rotatable table into the process chamber 56 and to receive the wafer boat 12, 14 from the process chamber 56 onto the rotatable table 16. In the cooldown position 26 the wafer boat handling device 10 may be configured to cool down a wafer boat 12, 14. In the transfer position 28 wafers may be transferred to and/or from the wafer boat 12, 14.

The effects and advantages of the wafer boat handling device 10 have been described in the summary section and these effects and advantages are inserted here by reference.

In an embodiment, of which an example is shown in FIG. 2, the wafer boat handling device 10 may be configured such that the second wafer boat support surface 20 of the rotatable table 16 is rotatable by the actuator from the cooldown position 26 to the transfer position 28 when a wafer boat 12, 14 from the first wafer boat support surface 18 has been loaded into the process chamber 56.

With this configuration of the wafer boat handling device 10 it is possible to have a first wafer boat 12 loaded into the process chamber 56, whilst a second wafer boat 14 at the same time can be cooled down in the cooldown position 26 and subsequently rotated to the transfer position 28 in which transfer position 28 wafers can be transferred to and from the second wafer boat 14. The second wafer boat 14 therefore does not have to wait for the first wafer boat 12 to be finished with processing before the second wafer boat 14 can be rotated to the transfer position 28. In this way, even though just to wafer boat support surfaces are available, valuable time can be saved because the cooling down of the wafer boat as well as the transferring of wafers in the cooled down wafer boat can be performed during the processing of wafers which are accommodated in the other wafer boat which is in the process chamber 56. The advantage of a reduced diameter of the wafer boat handling device 10 may be combined with a high production capacity.

In an embodiment, a rotational angle of the rotatable table 16 to rotate the wafer boat support surface 18, 20 from the cooldown position 26 to the transfer position 28 is enough to prevent heat transfer from a wafer boat 12, 14 which is in the cooldown position 26 to a part of a circumferential wall 32 of the wafer boat handling device 10 adjacent to the transfer position 28 to an extend as to keep the temperature of the part of the circumferential wall 32 adjacent to the transfer position 28 below 70° C., preferably below 50° C.

The circumferential wall 32 adjacent to the transfer position 28 may comprise a transfer opening 36 and/or a transfer door 38 for wafers to pass the circumferential wall 32. When the transfer position 28 would be too near the cooldown position 26, a hot wafer boat 12, 14 in the cooldown position 26 might have a negative impact on the transfer door construction. In order to withstand the high temperatures of a hot wafer boat 12, 14, the design of the transfer door 38 may become very complex and thus expensive. Optionally, the transfer door 38 may be actively cooled such that the wafer boat may be hot when transferred and the boat subsequently may be cooled down in the transfer position 28. By having the rotational angle between the cooldown position 26 and the transfer position 28, the circumferential wall 32 adjacent to the transfer position 28 will not become too hot, which means a more simple transfer door design is feasible. The rotational angle of the rotatable table 16 to rotate the wafer boat support surface 18, 20 from the cooldown position 26 to the transfer position 28 may be between 1° and 80°, preferably between 40° and 50°, more preferably substantially 45°.

In an embodiment, of which an example is shown in FIG. 1, the wafer boat handling device 10 may be configured such that the second wafer boat support surface 20 is in the cooldown position 26 when the first wafer boat support surface 18 is in the load/receive position 24. This means that the wafer boat handling device 10 can cool down a wafer boat 12, 14 in the cooldown position 26, simultaneously to processing a wafer boat 12, 14 in the process chamber 56.

A rotational angle of the rotational table 16 to rotate the wafer boat support surface 18, 20 from the load/receive position 24 to the cooldown position 26 may be between 120° and 240°, preferably between 170° and 190°, more preferably substantially 180°.

This means that when the first wafer boat support surface 18 is rotated from the load/receive position 24 to the cooldown position 26, the second wafer boat support surface 20 is rotated form the cooldown position 26 to the load/receive position 24. In other words, the wafer boat support surfaces 18, 20 swap places, and with them the wafer boats 12, 14 on these support surfaces 18, 20.

In an embodiment, the wafer boat handling device 10 is configured to subsequently:

load a first wafer boat 12 vertically from the first wafer boat support surface 18 which is in the load/receive position 24 into the process chamber 56,

cool down a second wafer boat 14 on the second wafer boat support surface 20 which is in the cooldown position 26,

rotate the rotatable table 16 to a rotational position in which the second wafer boat support surface 20 is in the transfer position 28,

transfer wafers to and/or from the second wafer boat 14, to rotate the rotatable table 16 to a rotational position in which the first wafer boat support surface 18 is in the load/receive position 24,

receive the first wafer boat 12 from the process chamber 56 on the first wafer boat support surface 18, and

rotate the rotatable table to a rotational position in which the second wafer boat support surface 20 is in the load/receive position 24.

Of the three functions of the wafer boat handling device 10, usually the processing of the wafers in the process chamber 56 is most time consuming. By configuring the wafer boat handling device 10 such that the cooling and the transferring are performed within the same time as the processing, the efficiency of the wafer boat handling device 10 may be improved. By having the transfer position 28 at a different position from the cooldown position 26 the added advantage is that heat from a hot wafer boat 12, 14 does not raise the temperature of the part of circumferential wall 32 adjacent to the transfer position 28 too high. Consequently, a transfer door 38 at the transfer position may have a more simple design, as is explained above in reference to another embodiment, which arguments also apply here.

In an embodiment, the wafer boat handling device 10 may further comprise a main housing having a circumferential wall 32 which may be provided with a transfer opening 36 at the transfer position 28 through which wafers can be transferred to and from the wafer boat 12, 14 that is accommodated on the wafer boat support surface 18, 20 which is in the transfer position 28. The wafer boat handling device 10 may further comprise a transfer door 38 configured to open the transfer opening 36 when the wafers are transferred, and to close of the transfer opening 36 when no wafers are transferred.

In an embodiment, the wafer boat handling device is provided with a wafer boat lift assembly having a vertically movable lift support member. The rotatable table 16 may have a lift support opening at both the first and the second wafer boat support surfaces 18, 20 through which the lift support member can pass the rotatable table 16 for accommodating the lift support member in a space between a lower side of the rotatable table 16 and an upper side of a bottom wall 34 of a main housing. The wafer boat lift assembly can transport the wafer boats 12, 14 to and from the process chamber 56. The lift support member can past the rotatable table 16 and lift the wafer boat 12, 14. When the wafer boat lift assembly has placed the wafer boat 12, 14 onto the wafer boat support surface 18, 20, the lift support member can again pass the rotatable table, such that the rotatable table can freely rotate without being obstructed by said lift support member. The wafer boat lift assembly may be part of the wafer boat handling device 10.

In an embodiment, the wafer boat handling device 10 may further comprise a vertically extending wall structure 46 mounted on the rotatable table 16. The vertically extending wall structure 46 may create and at least partially bound an associated vertically extending first wafer boat chamber 48 at the first wafer boat support surface 18, and may create and at least partially bound an associated vertically extending second wafer boat chamber 50 at the second wafer boat support surface 20.

These wafer boat chambers 48, 50 may form mini-environments wherein the wafer boasts 12, 14 are shielded from debris from each other.

In an embodiment, the wafer boat handling device 10 may further comprise a gas circulation system for supplying a gas to and withdrawing the gas from at least the first and/or the second wafer boat chamber 48, 50. The gas circulation system may be configured to cooldown the gas which is supplied to said wafer boat chamber 48, 50. Thus the cooling of the wafer boat 12, 14 in the cooldown position 26 may be effected.

The present disclosure also provides a vertical batch furnace assembly 54 comprising a process chamber 56 for processing wafers accommodated in a wafer boat, and a wafer boat handling device 10 according to the present disclosure. The wafer boat handling device 10 is positioned under the process chamber 56, and is provided with a wafer boat lift assembly configured to transfer a wafer boat 12, 14 from the wafer boat handling device 10 to the process chamber 56 and vice versa.

The effects and advantages of the vertical batch furnace assembly have been described in the summary section and these effects and advantages are inserted here by reference.

In an embodiment, of which an example is shown in FIGS. 3 and 4, the vertical batch furnace assembly 54 is provided with a substantially rectangular footprint having two opposite short sides 66 defining a width of the vertical batch furnace assembly and having two opposite long 68 sides defining a length of the vertical batch furnace assembly. The vertical batch furnace assembly 54 may further comprise at least one cassette in-out port 58, which may be arranged at one of the short sides 66 of the vertical batch furnace assembly 54. The vertical batch furnace assembly preferably comprises two cassette in-out ports 58, which may be arranged adjacent to each other . The vertical batch furnace assembly 54 may further comprise a cassette storage 60 configured to store a plurality of substrate cassettes each of which comprises wafers. The batch furnace assembly may include a cassette door opener device 70 and a cassette handler 62 which may be configured to transfer substrate cassettes between the cassette in-out port 58, the cassette storage 60 and the door opener device 70. The cassette storage 60 may be embodied as a cassette storage carousel. The vertical batch furnace assembly 54 may comprise one, or multiple cassette storage carousels, as is shown in FIG. 3. The vertical batch furnace assembly 54 may also comprise a wafer handler 64 configured to transfer wafers between a cassette in the door opener device 70 and a boat in the wafer boat handling device 10.

By having a substantially rectangular footprint and by having the cassette in-out port 58 arranged at the short side 66 of the vertical batch furnace, multiple of these vertical batch furnaces 54 can be placed adjacent to each other, as is shown in FIG. 5. The cassettes with wafers to be processed can be transferred to and from the assembly at the short side 66 of the vertical batch furnace 54. The other parts of the assembly 54 may be arranged in cascade behind the in-out port 58 such that the vertical batch furnace assembly 54 may have a certain maximum width. A width of less than 1.1 m is beneficial in view of interchangeability with other vertical batch furnace assemblies.

Finally, the present disclosure provides a method for handling wafer boats 10. The method comprises:

providing a vertical batch furnace assembly 54 comprising a process chamber 56 and a wafer boat handling device 10 which is positioned under the process chamber 56, wherein the wafer boat handling device 10 is the wafer boat handling device 10 according to the present disclosure;

providing the first wafer boat support surface 18 with an associated first wafer boat 12 loaded with wafers and the second wafer boat support surface 20 with an associated second wafer boat 14 loaded with wafers;

loading the first wafer boat 12 vertically from the first wafer boat support surface 18 which is in the load/receive position 24 into the process chamber 56; and

processing the wafers accommodated in the first wafer boat 12 in the process chamber 56, whilst simultaneously:

cooling down the second wafer boat 14 on the second wafer boat support surface 20 which is in the cooldown position 26;

subsequent to the cooling down, rotate the rotatable table 16 to a position in which the second wafer boat support surface 20 is in the transfer position 28;

transferring wafers to and/or from the second wafer boat 14; and

subsequent to the transferring, rotate the rotatable table 16 to a position in which the first wafer boat support surface 18 is in the load/receive position 24.

The effects and advantages of the method have been described in the summary section and these effects and advantages are inserted here by reference.

In an embodiment, the method may further comprise:

receiving the first wafer boat 12 from the process chamber 56 on the first wafer boat support surface 18; and

subsequently rotate the rotatable table 16 to a rotational position in which the second wafer boat support surface 20 is in the load/receive position 24.

After these method steps, the wafer boat support surfaces 18, 20 are swapped with respect to the start of the method. That means that the method herein described can be performed again. By repeating these steps continuously, the wafer boat handling device continuously receives wafers, processes these wafers, cools these wafers and delivers the processed wafers.

Although illustrative embodiments of the present invention have been described above, in part with reference to the accompanying drawings, it is to be understood that the invention is not limited to these embodiments. Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this description are not necessarily all referring to the same embodiment.

Furthermore, it is noted that particular features, structures, or characteristics of one or more of the various embodiments which are described above may be used implemented independently from one another and may be combined in any suitable manner to form new, not explicitly described embodiments. The reference numbers used in the detailed description and the claims do not limit the description of the embodiments nor do they limit the claims. The reference numbers are solely used to clarify.

LEGEND

-   10—wafer boat handling device -   12—first wafer boat -   14—second wafer boat -   16—rotatable table -   18—first wafer boat support surface -   20—second wafer boat support surface -   22—central vertical axis -   24—load/receive position -   26—cooldown position -   28—transfer position -   32—circumferential wall -   34—bottom wall -   36—transfer opening -   38—transfer door -   46—vertically extending wall structure -   48—first wafer boat chamber -   50—second wafer boat chamber -   54—vertical batch furnace assembly -   56—process chamber -   58—cassette in-out port -   60—cassette storage -   62—cassette handler -   64—wafer handler -   66—longitudinal end 

1. A wafer boat handling device, configured to be positioned under a process chamber of a vertical batch furnace, wherein the wafer boat handling device comprises: a rotatable table having just a first and a second wafer boat support surface, each configured to support a wafer boat configured to accommodate a plurality of wafers, wherein the rotatable table is rotatable by an actuator around a central substantially vertical axis to rotate the first and the second wafer support surfaces to: a load/receive position in which the wafer boat handling device is configured to load a wafer boat vertically from the rotatable table into the process chamber and to receive the wafer boat from the process chamber onto the rotatable table; a cooldown position in which the wafer boat handling device is configured to cool down a wafer boat; and a transfer position in which the wafer boat handling device is configured to allow transfer of wafers to and/or from the wafer boat.
 2. The wafer boat handling device according to claim 1, wherein the wafer boat handling device is configured such that the second wafer boat support surface of the rotatable table is rotatable by the actuator from the cooldown position to the transfer position when a wafer boat from the first wafer boat support surface has been loaded into the process chamber.
 3. The wafer boat handling device according to claim 1, wherein a rotational angle of the rotatable table to rotate the wafer boat support surface from the cooldown position to the transfer position is enough to prevent heat transfer from a wafer boat which is in the cooldown position to a part of a circumferential wall of the wafer boat handling device adjacent to the transfer position to an extend as to keep the temperature of the part of the circumferential wall adjacent to the transfer position below 70° C., or below 50° C.
 4. The wafer boat handling device according to claim 1, wherein a rotational angle of the rotatable table to rotate the wafer boat support surface from the cooldown position to the transfer position is between 1° and 80°, or between 40° and 50°, or substantially 45°.
 5. The wafer boat handling device according to claim 1, wherein the wafer boat handling device is configured such that the second wafer boat support surface is in the cooldown position when the first wafer boat support surface is in the load/receive position.
 6. The wafer boat handling device according to claim 5, wherein the wafer handling device is configured with the rotational table and the wafer boat support surface being rotatable from the load/receive position to the cooldown position over a rotational angle between 120° and 240°, between 170° and 190°, or substantially 180°.
 7. The wafer boat handling device according to claim 1, wherein the wafer boat handling device is configured to subsequently: load a first wafer boat vertically from the first wafer boat support surface which is in the load/receive position into the process chamber; cool down a second wafer boat on the second wafer boat support surface which is in the cooldown position; rotate the rotatable table to a rotational position in which the second wafer boat support surface is in the transfer position; transfer wafers to and/or from the second wafer boat; rotate the rotatable table to a rotational position in which the first wafer boat support surface is in the load/receive position; receive the first wafer boat from the process chamber on the first wafer boat support surface; and rotate the rotatable table to a rotational position in which the second wafer boat support surface is in the load/receive position.
 8. The wafer boat handling device according to claim 1, further comprising a main housing having a circumferential wall which is provided with a transfer opening at the transfer position through which wafers can be transferred to and from the wafer boat that is accommodated on the wafer boat support surface which is in the transfer position.
 9. The wafer boat handling device according to claim 8, further comprising a transfer door configured to open the transfer opening when the wafers are transferred, and to close of the transfer opening when no wafers are transferred.
 10. The wafer boat handling device according to claim 1, wherein the wafer boat handling device is provided with a wafer boat lift assembly having a vertically movable lift support member, wherein the rotatable table has a lift support opening at both the first and the second wafer boat support surfaces through which the lift support member can pass the rotatable table for accommodating the lift support member in a space between a lower side of the rotatable table and an upper side of a bottom wall of a main housing.
 11. The wafer boat handling device according to claim 1, further comprising a vertically extending wall structure mounted on the rotatable table and creating and at least partially bounding an associated vertically extending first wafer boat chamber at the first wafer boat support surface, and an associated vertically extending second wafer boat chamber at the second wafer boat support surface.
 12. The wafer boat handling device according to claim 11, further comprising a gas circulation system for supplying a gas to and withdrawing the gas from at least the first and/or the second wafer boat chamber, wherein the gas circulation system is configured to cooldown the gas which is supplied to said wafer boat chamber.
 13. A vertical batch furnace assembly comprising: a process chamber for processing wafers accommodated in a wafer boat; a wafer boat handling device according claim 1, wherein the wafer boat handling device is positioned under the process chamber, and is provided with a wafer boat lift assembly configured to transfer a wafer boat from the wafer boat handling device to the process chamber and vice versa.
 14. The vertical batch furnace assembly according to claim 13, provided with a substantially rectangular footprint having two opposite short sides defining a width of the vertical batch furnace assembly and having two opposite long sides defining a length of the vertical batch furnace assembly, wherein the vertical batch furnace assembly further comprises: at least one cassette in-out port arranged at one of the short sides of the vertical batch furnace assembly; a cassette storage configured to store a plurality of substrate cassettes each of which comprises wafers; a cassette door opener device; a cassette handler configured to transfer substrate cassettes between the cassette in-out port, the cassette storage and the door opener device; a wafer handler configured to transfer wafers between a cassette in the door opener device and a boat in the wafer boat handling device, wherein the width of the vertical batch furnace assembly is 1.1 meter or less.
 15. A method for handling wafer boats comprising: providing a vertical batch furnace assembly comprising a process chamber and a wafer boat handling device which is positioned under the process chamber, wherein the wafer boat handling device is the wafer boat handling device according to claim 1; providing the first wafer boat support surface with an associated first wafer boat loaded with wafers and the second wafer boat support surface with an associated second wafer boat loaded with wafers; loading the first wafer boat vertically from the first wafer boat support surface which is in the load/receive position into the process chamber; and processing the wafers accommodated in the first wafer boat in the process chamber, whilst simultaneously: cooling down the second wafer boat on the second wafer boat support surface which is in the cooldown position; subsequent to the cooling down, rotate the rotatable table to a position in which the second wafer boat support surface is in the transfer position; transferring wafers to and/or from the second wafer boat; and subsequent to the transferring, rotate the rotatable table to a position in which the first wafer boat support surface is in the load/receive position.
 16. The method according to claim 15, further comprising receiving the first wafer boat from the process chamber on the first wafer boat support surface; and subsequently rotate the rotatable table to a rotational position in which the second wafer boat support surface is in the load/receive position. 